1. Field of the Invention
The present invention pertains to actuators which comprise a piezoelectric diaphragm, including actuators which comprise a piezoelectric diaphragm and techniques for compensating for temperature-dependent behavior of a piezoelectric diaphragm.
2. Related Art and Other Considerations
Diaphragms can be used for many purposes such as, for example, an actuator in a pump or as a driving part of a mechanical actuator for other applications. While many different types of diaphragms exist and many materials have been utilized for diaphragms, piezoelectric elements have proven to be one of the more promising materials for diaphragm construction. A piezoelectric material is permanently-polarized and will produce an electric field when the material changes dimensions as a result of an imposed mechanical force. This phenomenon is known as the piezoelectric effect. Conversely, an applied electric field can cause a piezoelectric material to change dimensions. This phenomenon is known as electrostriction, or the reverse piezoelectric effect.
In accordance with the reverse piezoelectric effect, a piezoelectric diaphragm can deflect or change its degree of curvature upon application of an electric field. Example piezoelectric diaphragms, methods of making piezoelectric diaphragms, and pumps incorporating the same are described in PCT Patent Application PCT/US01/28947, filed 14 Sep. 2001; U.S. patent application Ser. No. 10/380,547, filed Mar. 17, 2003, entitled “Piezoelectric Actuator and Pump Using Same”; U.S. patent application Ser. No. 10/380,589, filed Mar. 17, 2003, entitled “Piezoelectric Actuator and Pump Using Same”, and simultaneously filed U.S. Provisional Patent Application 60,670,692), entitled “PIEZOELECTRIC DIAPHRAGM ASSEMBLY WITH CONDUCTORS ON FLEXIBLE FILM”, all of which are incorporated herein by reference.
Piezoelectric materials have many significant features and advantages. One potential disadvantage is that the behavior of piezoelectric materials can be temperature dependent. In a diaphragm formed with a piezoelectric layer, for example, apart from electric field considerations, the degree of curvature of the piezoelectric layer (and thus the diaphragm generally) can change as its temperature increases. For example, a piezoelectric element having a slight curvature or crown tends to flatten as its temperature increases. Such flattening or change of curvature of the piezoelectric may present a problem when the piezoelectric diaphragm is expected to perform in a consistently accurate manner. For example, if the piezoelectric diaphragm is connected or linked to an actuator whose movement or displacement must be accurately controlled, the flattening or curvature change of the diaphragm thwarts precise positioning of the actuator. In other words, if the degree of curvature of a piezoelectric diaphragm prior to application of the electric field changes from a nominal initial curvature to a more flattened initial curvature due to a factor such as temperature, the final degree of curvature of the piezoelectric diaphragm upon application of the electric field will not be the expected final degree of curvature.
What is needed, therefore, and an object of the present invention, is apparatus, method, and/or technique for compensating for temperature dependent behavior of a piezoelectric diaphragm.